Injector plunger



March 3, 1964 D. M. PARTRIDGE INJECTOR PLUNGER Filed June 13, 1961 INVENTOR lag/e iY/rtnqqe BY MQW ATTORNEY United States Patent 3,123,996 lNlEfl'iilR PLUNGER Bale M. Partridge, Grand Rapids, Mich assignor to General Motors Corporation, Detroit, Mich, a corpora= tion of Delaware Filed June 13, 1%1, Ser. No. 116,319 1 Claim. (61. 193-41) This invention relates to fuel injector pumps such as are used on Diesel engines, and particularly to the injector pump plunger.

Injector pumps of the type referred to comprise a pumping chamber within which a reciprocable plunger opcrates to create suiiicient fuel pressure that the fuel in the chamber will be forced past a normally spring closed injection valve and into the combustion chamber of the engine at the appropriate point in the engine operating cycle. The plunger is ordinarily mechanically driven by the engine on its pumping stroke, and the return stroke of the plunger is effected by a spring. Fuel under relatively low supply pressure is delivered to the pumping chamber via one or more ports which are traversed by the plunger, and during the pumping stroke the closing and reopening of these ports to start and terminate the fuel injection is controlled by providing a relief groove on the periphery of the plunger. The lateral extremities of the groove define the precise timing of the ports closing and opening. Also, since the start and/ or the ending or duration of injection is normally desired to be varied to suit engine power demands, one or both lateral extremities of the groove are formed so as to extend helicaliy of the plunger axis, and the plunger is rotatably adjustable to advance or retard opening and closing of the ports.

In order to obtain optimum uniformity in the production of such plungers as will insure good engine eiiiciency and speed control, the shape of the helixes must be very precisely formed and orientated about the plunger axis with reference to the means by which the plunger is adjustably rotated in eiiecting the aforementioned injection timing. Successive rough and finish machining operations are accordingly performed to bring all portions of the plunger to correct size, and to s.-ape and properly locate the helix with reference thereto. In forming the groove, a portion thereof adjacent one end of the helix is arranged to extend generally longitudinally of the plunger, which portion dually serves to provide clearance for the helix cutting and grinding tools, and to provid means for angularly locating the plunger during various of the machining operations.

Heretofore in the manufacture of such plungers it has been the practice to form the groove including its longitudinally extending portion with a relatively small diameter milling cutter, operated with its axis disposed radially of the plunger. This results in the lateral extrem' ies of this portion extending in planes non-radially of the plunge This has many disadvantages, including particularly that when locating against one side of this groove portion during subsequent machining operations on the plunger, only the relatively sharp edge at the side of this groove portion is relied upon for locating purposes, and the angular position of this edge relative to the helix and axis of the plunger will Change as the result of reducing the outer diameter of the plunger during machining.

I have discovered that by a slight redesign of the plunger groove, specifically the longitudinally extending portion thereof, the aforementioned disadvantages can be eliminated and a stronger and more economically manufactured plunger is obtained. I accomplish the improvement by forming the longitudinal groove portion with that side thereof which is adjacent the helix of the "Ice main portion of the groove in a plane extending radially of the plunger, and I extend the bottom of this longitudinal groove portion perpendicularly of such plane until it intersects the outer periphery of the plunger. As a result, the use of a larger milling cutter to form the groove is permitted, with the advantage of increased tool life, less de-burring at the edges of the groove is required, and cleaning of the plun er groove during manufacturing and at time of service is facilitated.

These and other objects and advantages of the invention will be more clearly understood from the following escription, having reference to the drawing wherein:

FlGURE l is a longitudinal cross-section through a unit fuel injector-pump of a well-known type used in internal combustion engines showing a plunger of my improved construction.

FIGURE 2 is an enlarged cross-sectional view of such a plunger as made prior to my invention, the section being taken in the area of the plunger relief groove and showing in broken outline the milling cutter in its position during forming of the groove longitudinal portion.

FIGURE 3 is a perspective fragmentary view of such a plunger with the prior art form of groove.

FEGURE 4 is a view similar to FIGURE 2, but illustrating in broken outline the use of a larger diameter cutter 'n the different location for forming the groove in accordance with my inve tion.

FlGURE 5 is a view similar .0 FIGURE 3 but showin g the improved groove construction.

The injector-pump illustrated in FIGURE 1 includes a pump body 1 into which fuel is supplied under pressure through an inlet fitting 2 and is conducted through passages (not shown) to an annular reservoir chamber 3 formed in a lower extension or nut 4- threadedly secured to the lower end of the body. In use, the nut 4 extends through a suitable opening in the cylinder head or other wall portion (not shown) of an internal combustion engine and terminates in a fuel discharge nozzle 5 within the firing space of the engine. Suitably supported within the nut and surrounded by the annular reservoir 3 is a bushing 6 which forms the pumping chamber '7 for a reciprocable and rotatable plunger 8. The particular pumping chamber bushing 6 shown has upper and lowe' fuel inlet and bypass ports 9 and 9 extendin through diametrically opposite sides thereof from the reservoir chamber 3. Opening and closing of these ports is controlled by the movement of the plunger, as will be more fully described hereinafter.

The outlet for injection fluid from the chamber 7 is shown by way of the longitudinal passage ltl through a spacer member ll which abuts the lower end of the bushing 6. Between this spacer and the nozzle 5 is a spring chamber member 12 containing a normally springclosed injection valve 13 of conventional form, and when this valve is forced open by fuel pressure developed in ping chamber '7 and passage 19 the fuel flows th ough the spring chamber, past a conventional antiblow-back valve 14, and through a longitudinal tip passage lS in the nozzle for discharge via one or more spray orifices or slots 16 at the lower end of the nozzle.

The plunger has its lower end section relieved on its periphery by an external groove 17 which, in the design shown, extends completely around the plunger. Connecting internm passages 18 and 19 within the plunger provide continuous communication between the groove 17 and the pumping chamber below the plunger. Accordingly, when either or both of the side ports 9 and 9' in the bushing register with the groove 17 there is communication between these ports and the pumping chamber, and the fuel pressure within the chamber below the plunger will be at the relatively low value (e.g. 40 psi.) of the injector-pump fuel supply. The lateral extremities of the groove are such, however, that during the pumping stroke of the plunger, both ports 9 and 9' can be maintained out of registry with the groove for a predetermined period to build up fuel pressure below the plunger to a value sufiicient to open the injection valve 13 and effect fuel discharge into the engine from the nozzle 5. In the position of the parts as shown in FIGURE 1, the plunger is at the upper limit of its stroke. \Vhen it is moved downwardly (as by cam actuation of follower member 29 against the force of plunger return spring 21) the fuel in the chamber 7 is bypassed into the reservoir chamber through the lower port 9' and, via the plunger passages 18, i9 and groove 17, through the upper port 9, until these ports are closed by the periphery of the plunger below and above the groove 17. The aforementioned injection pressure is then built up as the plunger continues its downward movement until the lower port 9' registers with the groove 17, causing the fuel in the chamber to be again bypassed to the reservoir chamber 3, with resultant drop in pump chamber pressure and reclosing of the injection valve 13.

The upper and lower lateral extremities 22 and 23 of the groove 17 are shown extending helically of the plunger axis, and by adjustably rotating the plunger by a pinion 24 (engaging a rack gear not shown), the start and finish of the injection period is adjusted. As is conventional, a fiat 25 is formed on the side of the plunger to provide for rotatably coupling thereto the pinion 24 Whose bore has a conforming fiat.

As previously mentioned, the helixes defining the lat eral extremities 22 and 23 of the plunger groove must be very precisely formed and oriented about the plunger axis with respect to the flat 25 to assure the desired timing of the injection. As best shown in FIGURE 3, the groove 17 is conventionally formed with a longitudinal extending portion 17. This portion 17 serves to provide clearance for the cutters and grinding tools used in shaping the helical edge 22 of the groove, and to provide a locating edge 26 for reference in angularly locating the plunger during the machining of the groove 17 and its fiat 25. Prior to my invention, the locating edge 26 and the groove portion 17 have been rough-formed with a milling cutter, shown in broken outline at 27 in FIGURE 2, Whose axis is coplanar with the longitudinal axis of the plunger so that it forms both lateral extremities 28 of the groove portion 17' on surfaces which do not extend radially of the plunger. Since it is desired to locate the pinion gear flat 25 symmetrical with and diametrically opposite the edge 26, the rough machining work to form the flat 25 is performed with the plunger angularly located in the grinding fixture against the relatively sharp edge 26. Subsequent rough grinding and finish grinding of the plunger external diameter adjacent the groove results in some shifting of the location of the control edge 26 angularly of the plunger axis by reason of the reduction in diameter which occurs during such machining. Then, when later finish grinding the flat 25 (which is done using a fixture which locates the plunger with reference to the rough-ground flat) the angular relation of the flat to the edge 26 and the helix 22 is no longer maintained as originally set. Error, as well as a rather unsatisfactory locating condition during finish grinding of the helix, results, as well as the other mentioned difiiculties in subsequently cleaning and de-burring the plunger.

This is avoided in the improved plunger shown in FIG- URE 5 wherein the longitudinally extending portion 17" is formed with its face 29 extending coplanar with the plunger axis and its bottom surface 30 extending substantially perpendicular from the latter to the external periphery of the plunger. This improved design may be conveniently formed as indicated in FIGURE 4 by using a larger diameter cutter 31 having its longitudinal axis oilset from the axis of the plunger. The pinion gear flat 25 can thus be located symmetrically and diametrically opposite the side or surface 29 which provides a relatively large area for angularly locating the plunger during the machine operations. Also since the plunger groove portion 17" is open on two sides rather than only one as in the case of the prior construction shown in FIGURE 3, it is more easily cleaned of residue after machining and during service overhauling. Likewise, the de-burring operation on this portion of the groove is facilitated and reduced in extent.

While only a single preferred embodiment of the invention has been disclosed, it is appreciated that numerous minor changes in the construction and arrangement of the parts may be made without departing from the spirit and scope of the invention as defined in the following claim.

I claim:

In a plunger for a fuel injector pump of the reciprocating plunger type having a pumping chamber with a plunger controlled side port, said plunger having an external groove registerable with said port during its pumping stroke, said groove comprising a first portion extending generally circumferentially of the plunger and an adjoining second portion extending generally longitudinally of the plunger, said groove first portion having a lateral extremity disposed generally helically of the plunger axis and terminating with a generally longitudinally extending lateral extremity of said groove second portion, said last named extremity being a surface substantially coplanar with the longitudinal axis of the plunger, said groove second portion having its bottom fiat surface extending generally perpendicular to said surface substantially coplanar with the longitudinal axis of the plunger and intersecting the ungrooved periphery of the plunger adjacent said groove.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,234 Meiswinkel Sept. 29, 1942 2,547,174 Rogers Apr. 3, 1951 2,565,681 Fleck et al. Aug. 28, 1951 2,674,950 Underwood Apr. 13, 1954 2,696,786 Fleck et al. Dec. 14, 1954 2,890,657 May et al. June 16, 1959 2,969,738 Ulbing Jan. 31, 1961 

